1. Technical Field
The present invention relates to braking devices, and more particularly to a braking device that generates less cogging torque and noise.
2. Description of Related Art
In a braking device, when the permanent magnet of its rotor moves with respective to the slot of its stator, the gap reluctance varies with the changing magnetic flux and magnetic energy in the magnetic circuit, and as a result vibration as well as noise can generate. As known in the art, the consequent noise and cogging torque have significantly adverse impact on the performance of the braking device.
A conventional braking device primarily comprises a flywheel, a substantially circular rotor that is set on one lateral of the flywheel, and a stator that is deposited in a central hole of the rotor. The stator has a core that is provided with a plurality of outward extending teeth. Each of the teeth has a coil wound therearound. FIG. 1 shows periodic variation of cogging torque in a conventional braking device. As can be seen clearly, the average cogging torque is about 86.8 mN-m. In other words, such a braking device when operating can generate significant cogging torque and in turn disturbing noise.
For minimizing cogging torque, sonic manufacturers use plural permanent magnets to form the rotor for braking devices with a plurality of magnetic poles provided by the rotor, and use plural round silicon steel sheets to form the stator, wherein these silicon steel sheets are stacked in a specific deflection angle and fastened as a whole. The stator is peripherally formed with a plurality of oblique slots for receiving coils. The rotor and the stator such configured can generate a deflecting magnetic field that serves to eliminate vibration and the noise caused by cogging torque generated during the braking device's operation. However, this existing approach makes the braking device structurally Complicated and thus requires more manufacturing costs.
Therefore, the conventional braking devices need to be improved.